Author: Assmann, R.W.
Paper Title Page
WEPMU020 LHC Collimator Controls for a Safe LHC Operation 1104
  • S. Redaelli, R.W. Assmann, M. Donzé, R. Losito, A. Masi
    CERN, Geneva, Switzerland
  The beam stored energy at the Large Hadron Collider (LHC) will be up to 360 MJ, to be compared with the quench limit of super-conducting magnets of a few mJ per cm3 and with the damage limit of metal of a few hundreds kJ. The LHC collimation system is designed to protect the machine against beam losses and consists of 108 collimators, 100 of which are movable, located along the 27 km long ring and in the transfer lines. Each collimator has two jaws controlled by four stepping motors to precisely adjust collimator position and angle with respect to the beam. Stepping motors have been used to ensure high position reproducibility. LVDT and resolvers have been installed to monitor in real-time at 100 Hz the jaw positions and the collimator gaps. The cleaning performance and machine protection role of the system depend critically on the accurate jaw positioning. A fully redundant survey system has been developed to ensure that the collimators dynamically follow optimum settings in all phases of the LHC operational cycle. Jaw positions and collimator gaps are interlocked against dump limits defined redundantly as functions of the time, of the beam energy and of the beta* functions that describes the focusing property of the beams. In this paper, the architectural choices that guarantee a safe LHC operation are presented. Hardware and software implementations that ensure the required reliability are described. The operational experience accumulated so far is reviewed and a detailed failure analysis that show the fulfillment of the machine protection specifications is presented.